Cultured human adipocytes precursors (HAPs) are a promising culture system for investigation of inherent differences in cellular metabolism in obesity and diabetes. HAPS were established in culture from the stromal vascular fraction of collagenase digests of abdominal subcutaneous fat. In order to study an acute action of insulin on these cells, a method for measuring initial rates of glucose transport in confluent monolayers of HAPS was developed. Insulin stimulation of glucose transport was maximal in 30 min. and reversed by addition of anti-insulin antibody. Insulin stimulated glucose transport in HAPs with a mean (n-5) ED50 of 3 x 10 to the -9M insulin and the maximum insulin stimulated rated (137.5 (plus or minus) 10.5 nL/sec.mg) was twice basal (63.4 (plus or minus) 9.8 nL/sec.mg). Mature adipocytes may still reflect the in vivo milieu at the time of biopsy. An acute action of insulin in HAPs has been defined that can now be compared to similar data obtained for mature adipocytes from the same biopsy. Thus, this system may provide a tool for distinguishing between environmentally and genetically determined alterations in cellular metabolism that contribute to the increased insulin resistance associated with obesity and diabetes.